System for augmenting the coverage, information and robustness of automatic identification devices of ships

ABSTRACT

A system for augmenting the coverage, information and robustness of an automatic identification system of ships incorporates standard AIS-type means, satellite links, coastal stations and processing centers handling the coordination of the means (maximizing the coverage of the system in time) and the processing of the data (merging of different information to create extended context information). The system implements a scheduling algorithm for the resources mobilized, in order to optimise the coverage by ensuring a given level of redundancy for the purposes of reliability and responsiveness of the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to foreign French patent applicationNo. FR 10 02952, filed on Jul. 13, 2010, the disclosure of which isincorporated by reference in its entirety.

FIELD OF THE INVENTION

The object of the invention relates to a system and a method foraugmenting the coverage, information and robustness of automaticidentification systems, of AIS (Automatic Identification System) type,with which ships are equipped, intended for users on land or at sea,with no geographic limitation.

Hereinafter in the description, the expression “local context”designates a set of information relating to a local area, such as thepresence of ships, their position and their specific characteristics.The expression “local AIS context” designates the local contextinformation obtained by an AIS receiver, within a radius whichcorresponds to the very high frequency or VHF range. The expression“extended context” designates context information that is augmented interms of range, content and reliability. The content may be augmentedwith, for example, information relating to objects that are notcooperating in the AIS sense, such as other ships or hazards fornavigation: containers or, more generally, drifting objects.

An AIS cell corresponds to an area in which the AIS communications of aset of AIS transponders, embedded on ships or coastal stations, areself-organised and within the limit of VHF range.

The expression “global and dynamic coverage” is used to define a set ofAIS cells which are federated by the system according to the inventionusing so-called reference ships and coastal stations located in thedifferent cells.

A ship that has an AIS-type transponder, for exchanging information withvarious ships equipped with an AIS receiver or transponder, andsatellite communication means, for exchanging with a processing centre,can be activated as reference ship for a time period T.

A reference ground or coastal station is a station provided with an AIStransponder, for exchanging information with the various ships equippedwith AIS receiver or transponder and located in VHF range, andterrestrial communication means for exchanging with a processing centre.

A land-based processing centre will receive a set of information fromvarious information sources, such as the coastal stations, the referenceships, radar stations, satellite imaging, for processing andconsolidating the local contexts in order to produce extended contextinformation. The extended context information is then broadcast to saidstations and to the reference ships. A processing centre is associatedwith an area or with a geographic coverage.

The verb “consolidate” covers the action of collating and cross-checkingthe information collected by the different reference ships, by thecoastal stations, or other observation means such as radars or satelliteimaging, as will be detailed hereinbelow.

The AIS is an automatic identification system of the ships (MMSIregistration, position, heading, speed, etc.) which are in directvisibility via a VHF link, i.e. within a radius of 20-30 nautical miles,which can be used to estimate the local context, producing more enrichedinformation than that obtained with a radar. The main applicationsrelate to the prevention of collisions at sea, the monitoring oftraffic, navigation assistance, and, in the future, sea search andrescue missions.

Work and trials conducted in the USA and in Norway, for example, relateto the reception by satellite of the AIS signals transmitted by theships, in order to have global information over a wide coverage.However, the waveform and the time-division multiple access mode(automatic organisation of the TDMA) of the AIS, designed for cells witha radius of 50 km, lead to multiple interferences of the useful signalson a receiver embedded on a satellite covering a wide area and thereforereceiving a large number of signals originating from different cells byAIS VHF channel.

Without requiring specific satellites to be deployed, the proposedsystem according to the invention allows for a global coverage, based onexisting AIS infrastructures, and produces reliable and enrichedinformation.

The system can merge various information sources, from observation anddetection means on land or otherwise embedded on ships, aircraft(aeroplanes, drones) or satellites. In addition to the global coverageand increased reliability, this composite information can then be usedto identify incorrect AIS transmissions and non-cooperative objectswithout AIS transmitters.

BACKGROUND OF THE INVENTION

The prior art describes known AIS extension solutions.

A first solution consists in receiving AIS signals from all the shipspresent in an area, onboard specific satellites. This entailsdifferentiating the AIS messages transmitted by ships in differentcells, typically using an antenna implementing a spatial filtering witha very fine cellular coverage. This first solution, based on specificsatellites with complex antennas, is very costly.

A second solution relies on the deployment of coastal stations and theaggregation of the information supplied by a coastal coverage. Thissecond solution generally does not cover more than an area locatedwithin 50 km of the coasts.

REFERENCES USED

-   -   Ai: coverage area i    -   Nref: reference ship    -   Nrefi: reference ship i    -   Nt: ship equipped with an AIS transponder    -   Nr: ship equipped with an AIS receiver    -   Ni: ship i    -   Rm: shipping route    -   Sci: coastal station i; which are a priori all considered as        reference coastal stations, i=1, 2, . . . coastal station No.,    -   Cti: processing centre    -   Ls: satellite link    -   Zi: AIS cell    -   Mci: consolidated information Mc for an area i, the set of        consolidated information Mci.    -   Generally, the expression “reference station” equally designates        the reference ships and the reference coastal stations.

SUMMARY OF THE INVENTION

The identification system according to an embodiment of the inventionprovides an extended, global coverage, without geographic limitation.For this, the system according to the invention incorporates standardAIS-type means, satellite links, coastal stations and processing centreshandling the coordination of the means (in order to maximise thecoverage of the system in time) and the processing of the data (mergingof different information to create extended context information). Itnotably implements a scheduling algorithm for the resources mobilised,in order to optimise the coverage by ensuring a given level ofredundancy for the purposes of reliability and responsiveness of thesystem.

An object of the invention relates to a system for augmenting thecommunication or automatic identification range of an AIS-type system,said system comprising, in combination, at least the following elements:

-   communication means allowing for the exchange of information between    the various elements forming said system,-   one or more land-based processing centres Cti comprising:    -   communication interfaces I_(I), I_(Sat), for the exchange of        information with different users, the reception of information        from reference ships Nrefi, and for the broadcasting of        consolidated and extended information Mci after processing to        said reference ships Nrefi, and coastal stations Sci.    -   a set of processors P suitable for merging information of        different types,    -   one or more databases D,    -   a memory M for storing information with a view to its        processing,-   one or more terrestrial stations Sci linked with one or more    processing centres Cti by communication means Ri, allowing for an    exchange of information,-   one or more ships elected as reference ships Nrefi for a given time    period T, said reference ships Nrefi communicating with the    processing centres Cti by said satellite means, and with ships in    VHF range,-   ships Nt, Nr provided with at least means for receiving information    broadcast by a reference ship located in VHF range and/or reference    coastal stations Sci in VHF range

A processing centre Cti has one or more interfaces I_(G) for receivinggeo-referenced observation/detection data, and said set of processors Pis suitable for aggregating the data from different reference ships andfrom coastal stations with geo-referenced data.

Another embodiment of the invention relates to a method for augmentingthe range of an AIS-type system, said method being implemented in asystem comprising the characteristics of the aforementioned systemingcharacterized in that it comprises at least the following steps:

-   -   defining one or more reference ground stations Sci, and one or        more reference ships Nrefi,    -   for a processing centre Cti controlling a given coverage area        Ai,        -   for each time period T or time slice of a given duration:            -   retrieving and accumulating various current local AIS                contexts (for the time period T concerned) detected by                the reference stations, reference ships Nrefi or                reference coastal stations Sci, coming under the                coverage area of the processing centre,            -   consolidating the AIS information, local context by                local context, by incorporating in a database D any new                information specific to said ships (ship identification,                position, heading, speed, etc.),    -   formatting for each reference station (ship or coastal station)        Nrefi or Sci having to broadcast this information:        -   for a configured visibility radius, formatting a specific            database Mci taking the information on objects in the global            context database, within a given radius relative to the            position of the reference station Nrefi or Sci scheduled for            the broadcast,

-   transmitting said formatted information Mci to said reference    station or stations Nrefi or Sci, via satellite links Ls or via    terrestrial communication means Ri,

-   broadcasting of the global context information to users on land by    using terrestrial communication means Ri,    -   for a reference ship Nrefi,        -   collection of the local AIS context and transmission to the            processing centre Cti via satellite link Ls,        -   broadcasting of the extended context Mci via AIS-type            channel to the ships or the objects equipped with an            AIS-type receiver located within a cell defined by the VHF            range,    -   for a reference coastal station Sci,        -   collection of the local AIS context and transmission to the            processing centre Cti via terrestrial communication means            Ri,            -   broadcasting of the extended context Mci via AIS-type                channel to the ships or the objects equipped with an                AIS-type receiver located within a cell defined by the                VHF range.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the device according to the inventionwill become more apparent from reading the description of an exemplaryembodiment given as a nonlimiting illustration, with appended figureswhich represent:

FIG. 1, a example of the distribution of the cells for a number of shipsfollowing a predefined maritime shipping route,

FIG. 2, the sequencing of the operations implemented in the case of thesystem comprising reference ships and processing centres, and

FIG. 3, an example of sequencing of the operations executed in the caseof a coastal station acting as reference for ships in VHF range.

DETAILED DESCRIPTION

In order to give a good understanding of the principle implemented inthe extended AIS system according to an embodiment of the invention, thefollowing example will be given in the context of a number of shipsbelonging, for example, to different AIS cells, a cell Zi being definedby the VHF communication range limit between the ships. The system givenas an example will include ships equipped with AIS transponders, shipsconfigured as reference ships for a given time period, coastal stationsand processing centres.

The AIS system or any other device operating on the AIS principleautomatically controls the allocation of the communication channel (TDMAtime slot and frequency channel) between the various transponders. Thus,the system according to an embodiment of the invention will be able toacquire different information corresponding to a set of local contexts,and a consolidation will be prepared in the processing centres.

FIG. 1 illustrates, for a given time period (defined time slice):

-   -   a specific shipping route R_(m) followed by a set of ships, Ni.        In this set of ships, some will be dynamically designated, for a        time period T, as reference ship Nrefi,    -   a number of reference coastal stations Sci,    -   three yachts Yri, for example isolated, also declared as        reference ships Nref,    -   a ship Ne leaving a cell according to a heading and a speed,        which will be declared as reference ship for a subsequent time        period in order to extend the global coverage. Use is made, for        example, of the information contained in a database combining,        for an identity Idnav of a ship, its navigation route Rnav, in        order to define the time slice T or period for which this ship        can be configured as reference ship (by the processing centre        controlling the area where the ship is located). When the ship        does not follow a predefined route, it is possible to use        heading and speed data to predict its route in the short term.        To serve as a reference, this ship must have a satellite        communication link,    -   a number of land-based processing centres Cti, a land-based        processing centre Cti controlling a given area Ai, an area Ai        being, for example, represented in FIG. 1 by the bold ellipse, a        centre comprising, for example as detailed in FIG. 2, the        following elements:        -   communication means, notably interfaces I_(sat), for            implementing satellite links for receiving information from            the reference ships Nrefi, and for broadcasting the            consolidated and extended information Mci after processing            by the centre to the reference ships Nrefi,        -   terrestrial communication means Ri for receiving information            from the reference coastal stations Sci, and for            broadcasting the consolidated and extended information Mci            after processing to these reference stations,        -   one or more interfaces I_(G) for receiving            observation/detection geo-referenced data by external means            such as radars, imaging, or even location systems (GPS            type), not represented in the figure in the interests of            simplicity,        -   internet-type interfaces I_(I) (FIG. 2), for example, for            the exchange of information with different users (for            example, monitoring, etc.),        -   a set of processors Pi, P₁, P₂, . . . suitable for merging            the information of different types and, possibly, for            aggregating the data concerning different local AIS contexts            originating from all the ships in AIS range of the reference            ships or the coastal stations, with other data, for example,            geo-referenced data,        -   one or more databases D,        -   a memory M, for the storage of the information with a view            to its processing which is linked with the processors.

The system of satellite communication means, in this example, issituated outside the processing centres and consists of a terminal 10arranged on a reference ship N_(ref), the satellite S and satelliteground stations I_(S) and the satellite link Ls represented in FIG. 2 bythe arrows 7, 8.

Without departing from the context of the invention, the terminal 10could be incorporated in the electronics of the AIS, and the satellitestations in the processing centres Cti.

Each of the ships Ni is equipped with an AIS terminal acting as atransmitter and receiver, some of these ships having a digital satellitelink. The transmission rate is, for example, 9600 bauds or more, the twoVHF frequencies commonly used being 161.975 MHz (maritime channel 87B)and 162.025 MHz (maritime channel 88B), which are reserved for thisapplication.

An AIS transponder comprises a transmitter and one or more receivers.The number of receivers is, for example, chosen according to the desiredredundancy for the system in order to avoid a loss (message collision)of information from ships. The AIS terminal also includes a satellitepositioning system and a control screen. An AIS transponder embedded ona ship is interfaced with the onboard instruments, such as the compass,the heading change indicator, etc.

Some ships Nr may be equipped only with an AIS receiver. They cannotsignal their position by AIS channel, but can benefit from the extendedcontext information which is broadcast by a reference ship or areference station in VHF range.

Any ship equipped with a satellite link Ls and an AIS transponder can beconfigured as reference ship Nref. It transmits the AIS context locallydetected with the AIS receiver (identification and position of the shipsprovided with an AIS transponder and present in the area), and possiblyadditional information (radar tracks, text message locating localisedobjects, hazards such as drifting containers), via a satellite link Lsto a land-based processing centre Cti which controls the area in whichthe ship is located to process this information. The informationtransmitted may contain the following information: the numberidentifying the ship, the navigation status, the route, the speed of theship, the change of heading speed, the longitude and latitude, the trueheading, etc. (collected from the local AIS cell).

After the different information sources have been processed on theground, the global and extended context information Mci (relating to areference station) can be broadcast by a reference ship Nrefi or acoastal station Sci via the AIS channel, from an AIS transponder.

The system (ships, ground stations and processing centres) includesatellite links notably allowing communication between the referenceships and the processing centres, and terrestrial communication networktype links between the reference ground stations or reference coastalstations and the processing centres.

The global context may include the AIS-type information, andgeo-referenced information relating to an unidentified objects,localised hazards, etc.

Operation of the System According to the Invention

The system will choose and schedule a number of reference ships Nrefi,and reference ground stations or coastal stations Sci, from all theships equipped with satellite communication means and from all theland-based coastal stations, according to the coverage need, given theknown position of the ships, their route and their scheduled movement.The course and the scheduling of professional and commercial ships aregenerally predefined and can be stored in a database.

The processing centres Cti can be coordinated, for example in two ways,to split the processing load by geographic area.

In a first mode of coordination of the processing centres, calledcentralised mode, a main particular centre Ctp dynamically orchestratesthe partitioning of the coverage and the allocation of the areas Ai tobe controlled by all the processing centres according to theiravailabilities and their computation powers. To ensure the reliabilityof the system, this main centre may be redunded in order to detect andovercome any failures.

In a second coordination mode, called self-organised mode, eachprocessing centre Cti determines all the active processing centres withtheir respective processing capabilities, and coordinates with the otherprocessing centres to partition the coverage area and allocate a sectoror area Ai for each processing centre.

Regardless of the mode of coordination of the processing centres used tosplit the coverage area and the processing of the corresponding data,the information identifying Id(Cti, Ai) which centre Cti controls whichgeographic area Ai, must be transmitted to the reference ships Nref andto the reference coastal stations. These reference ships and stationscan then transmit the collected local AIS context information to theprocessing centre or centres corresponding to their respective area Ai.

The movement of the ships causes them to cross reference ships Nrefi,which are in VHF radio range corresponding to approximately 50 km.

Any ship Ni provided with an AIS transponder newly detected by areference ship Nrefi or a coastal station can serve as referencestation, if it has satellite communication means, in order to augmentthe geographic coverage, the reliability and the responsiveness of thesystem.

The coverage of the system thus expands dynamically with the movementsof the ships able to be configured as reference ships Nref.

Initially, in the absence of any reference ship, the coverage is definedby the association of the individual coverages of the coastal stationsSci. The detection and activation of reference ships makes it possibleto extend the coverage.

A ship Nt, provided with an AIS transponder and a satellite link, whichdoes not detect any other reference station within its local AISperimeter, may be declared to a processing centre Cti to be configuredas reference ship Nref in order to augment the global coverage of thesystem, that is to say allow a relaying (acquisition of the localcontext and broadcasting of the extended context) of the informationwithin a perimeter that is greater than that usually defined by the AISrange.

The ships Nr equipped with simple standard AIS receivers receive theconsolidated global context information Mci via AIS channel, which isbroadcast by the reference stations, namely either the reference shipsNrefi, or the reference ground stations Sci.

For users at sea, the extended context information Mci for a local areaZi is derived from the global context information Mc, by being limitedto a certain perimeter around the reference station concerned, in orderfor the extended information bit rate to be compatible with the bit rateavailable on the AIS channel.

The global context information Mc can be broadcast partially for eacharea or as a whole to users on land, via network means Ri, ofterrestrial or other type.

FIG. 2 illustrates an example of sequencing for the exchanges ofinformation between a reference ship Nref and a processing centre Ct₁ ina system comprising ships Nt with an AIS transponder(transmitter/receiver), one ship Nr with a simple AIS receiver, and twoprocessing centres Ct₁, Ct₂.

A reference ship Nref communicates with the processing centres via asatellite link Ls and ground means Is₁ (satellite communication groundstation) which may be common to a number of processing centres.

The sequencing of the operations implemented within the system accordingto the invention may be, in the case of an exchange between a referenceship and the processing centre, as follows:

-   -   1—the AIS transponders (transmitter/receivers) with which the        ships Nt are equipped broadcast their AIS information, within        the AIS cell Zi with which they are in VHF range, in order to        establish a context local to an AIS cell,    -   2, 3, 4—the reference ships Nrefi located in this cell Zi        receive these AIS messages and transmit this local context via        satellite link Ls, via a satellite S to the processing centres        Ct₁, Ct₂ via the interface modules Isat, and a terrestrial        communication network Rj, the satellite links implementing, for        example, Inmarsat or Thuraya terminals and systems,    -   5—all the local contexts corresponding to different AIS cells        are merged in the processing centres Ct₁, Ct₂, possibly with        other sources of information (radar, imaging), by means of one        or more processors Pi with which the processing centres Ct₁,        Ct₂, are equipped, and so on,    -   6, 7—the information Mci consolidated in a processing centre Ct        is returned via the satellite link Ls to a reference ship Nref        responsible for broadcasting it locally,    -   8—the consolidated context information Mci received by the        reference ships, Nref, is locally broadcast, 9, via AIS channel,        to all the AIS terminals in VHF range.

FIG. 3 diagrammatically represents the sequencing of the exchanges witha coastal station Sci which acts as reference station:

-   -   11—the AIS transponders of the ships Nt broadcast their AIS        information, making it possible to establish the context local        to an AIS cell,    -   12—the reference coastal station or stations Sci receive all the        AIS messages, transmit this local context by terrestrial network        R, to the corresponding processing centre Ct₂, i.e. to the        processing centre which controls the area under which the        station comes,    -   13—the local contexts originating from the AIS cells are merged,        in the processing centres, by means of processors, with other        information sources as explained previously,    -   14—the consolidated information Mci is returned by terrestrial        network from the processing centre to the reference coastal        station,    -   15—the reference coastal station broadcasts the locally        consolidated information by AIS channel, to all the types of AIS        terminals in VHF range.        Other Variants

According to one embodiment, allowing for a better reliability andresponsiveness of the system, the system can allocate the “referencestation” status to a set of co-located ships, that is to say, shipspositioned in one and the same AIS cell Zi delimited by a given radiorange.

The repetitive broadcasting of the consolidated global contextinformation by AIS channel can be done by just one of these co-locatedships or by a set of these ships by using a shared access mode such asTDMA which allows for an alternation in time by a set of these ships.

According to one implementation of the invention, the system can be usedto detect inconsistencies in the information transmitted, or else afailure in the operation of the communications for a given ship.

For example, taking the case of two reference ships: a ship A and a shipB which are in VHF range, in one and the same cell, the processingcentre which controls the area or cell in which the ships are locatedcan decide that the ship A will monitor the information Mci (informationrelating to the area derived from the global context) transmitted by theship B. The processing centre transmits the same consolidatedinformation Mci to the two ships A and B. If A is configured to monitorthe information transmitted by B, it will monitor the consolidatedinformation that B broadcasts via the AIS channel to the ships in VHFrange. To this end, the terminal of the ship A implements means(software or hardware) for determining the identity of the ship B andthe content of the information that B broadcasts. This applies in thesame way to coastal stations.

A reference station or ship implementing processing means and processingalgorithms can thus monitor the correct broadcasting of the informationby another reference station or ship.

A reference station or ship can then be configured, by choice to:

-   -   collect the local AIS context,    -   broadcast the consolidated global information after processing        on the ground,    -   check the correct broadcasting of the global information by        another reference ship/station.

According to another implementation of the invention, the system canalso be used to check the consistency of the AIS information transmittedby a ship. For example, when a ship broadcasts an AIS message includingincorrect position information, the system can detect that this positionis not the correct position when this position does not geographicallycome under the AIS cell Zi of the reference ship or station havingpicked up the AIS message, or even when the AIS message has not beenpicked up by a reference station or ship close to the positionedconcerned.

According to another implementation of the invention, the system canalso be used to check the correct operation of the AIS transponder ofeach ship. A ship equipped with an active AIS transponder should appearwith its position, within the extended context, which is broadcast by areference station or ship. The AIS terminal can therefore check theconsistency between the GPS position known onboard and the position ofthe ship obtained from the consolidated context information. Amalfunction of the AIS transponder can thus be detected.

According to another implementation of the invention, the AIS messagesfrom the ships detected by the system can be used to facilitate andenhance the acquisition of other AIS messages picked up by a receiverembedded on an aircraft or a satellite, by generating replicas of theknown AIS messages to subtract them from the received signal accordingto the known Signal Cancelling technique. The AIS transmissions from theships detected by the system are entirely known, equally in terms ofcontent, of timing and of geographic origin of the messages. Theprocessing of the AIS signal received from an aircraft or a satelliteconsists in virtually subtracting the known AIS transmissions, to reducethe number of interfering signals. This processing can be done locallyonboard or on ground.

Data Processing Algorithm for Generating the Global Context:

For a processing centre Cti controlling a given area Ai (local,regional, national, continental, etc.), the processing algorithm willexecute the following steps:

-   -   for each time period T (time slice of a given duration: 1-3        minutes, for example):        -   retrieving and accumulating (storing in time for one and the            same reference station) various current local AIS contexts            (for the time period T concerned) detected by the reference            stations, reference ships Nrefi or reference coastal            stations Sci, coming under the coverage area of the            processing centre,        -   consolidating the AIS information, local context by local            context, by incorporating in a database D any new            information (ship identification, position, heading, speed,            etc.),        -   if necessary, merging this global AIS information with the            available additional data (radar, optical observations, text            messages on the location of new hazards, etc.),    -   a formatting step for each reference station (reference ship        Nrefi or coastal stations Sci) having to broadcast this        information:        -   for a configured visibility radius, formatting a specific            database Mci taking the information on objects in the global            context database Mc, by limiting itself to the ships and            objects located within a given radius relative to the            position of the reference station Nrefi or Sci scheduled for            the broadcast.

Once the global context is generated, the method will implement thefollowing steps:

-   -   a step of transmitting said formatted information Mci to said        reference station or stations Nrefi or Sci, via satellite links        Ls or via terrestrial communication means Ri,    -   a step of broadcasting the global context information to users        on land by using terrestrial communication means Ri,        -   for a reference ship Nrefi,            -   the collection of the local AIS context and transmission                to the processing centre Cti via satellite link Ls,            -   the broadcasting of the extended context Mci via                AIS-type channel to the ships or the objects equipped                with an AIS-type receiver located within a cell defined                by the VHF range,        -   for a reference coastal station Sci,            -   the collection of the local AIS context and transmission                to the processing centre Cti via terrestrial                communication means Ri,            -   the broadcasting of the extended context Mci via                AIS-type channel to the ships or objects equipped with                an AIS-type receiver located in a cell defined by the                VHF range.

The movement prediction horizon for a ship is very variable.

Professional or merchant ships respect departure and arrival timetables,and follow predefined routes. Their movement is therefore predictable inthe long term. The signalling of a delay or of a change of route and/orspeed also makes it possible to correct the long-term prediction.

On the other hand, a fishing boat is more free in its movements. Apleasure boat is even more changeable, and its prediction horizon isreduced to a few hours at best.

For each time period, the coverage is defined by the association of AIScellular coverages corresponding to the set of reference stations (shipsor coastal stations) selected.

Reference Ship/Station Scheduling Algorithm

For a processing centre Cti controlling a given area Ai or coverage(local, regional, national, continental, etc.)

Initialisation:

initialisation by declaration of the coastal stations Sci as referencestations loop, at the rate of the time period T: projection of thepositions of the ships identified by the system:   for each ship,   foreach future time period T + dt, up to the prediction horizon for the  ship     projecting the position, speed and heading, given theavailable    information (predicted date and time of departure, ofarrival,    route, last signalling) determination of the eligible shipsNeli:  for each future time period T + dt   for each ship having themeans mentioned previously allowing it to   be used as reference shipNref,    if the ship (projected trajectory) departs from the associatedAIS    cell Zi or coverage defined for the time period T, then it is a   priori eligible selection of the reference ships Nrefi:  iterating,for the desired redundancy level   for each future time period T + dt   for each eligible ship,     searching to see if other eligible shipsare in the     immediate vicinity (in AIS/VHF range), and selecting the    best according to a previously fixed criterion chosen from     thefollowing list: commercial ship, pricing, route,     limitation onchanges of configuration (reference ship     activation) for each ship,etc.     removing the selected ship from the list of eligible ships   updating the definition of the coverage withdrawing the referenceships Nrefi:  for each future time period T + dt   for each referenceship Nrefi,    searching to see if other ships or reference coastalstations Sci    are in the immediate vicinity (in AIS/VHF range), andidentifying    the N best (according to various criteria: commercialship,    pricing, route, limitation on changes of configuration for each   ship, etc.), N defining the desired redundancy level    removing theunselected ships from the list of reference ships   updating thedefinition of the coverage.

The algorithm can be applied immaterially for scheduling the referencestations (ships or coastal stations) used:

-   -   to collect the local AIS information, and to broadcast the        consolidated global context information    -   to solely collect the local AIS information    -   to solely broadcast the consolidated global context information    -   to check the correct broadcasting of the consolidated global        context information, by another reference ship/station.

The commercial ships whose navigation courses are scheduled, areimplicitly prioritised to serve as reference station, because of theirextended prediction horizon.

The system according to the invention notably offers the followingadvantages:

-   -   it allows to widen the coverage for collection and broadcasting        of information without geographic limitation, and therefore to        have a global coverage,    -   it allows to improve reliability and detection responsiveness,    -   it offers automatic and dynamic management of the allocation of        the reference stations (ships or coastal stations), to optimise        the coverage and the redundancy level for the reliability and        the responsiveness of the system,    -   the content of the information is augmented in range and in        nature, with the detection of objects that are non-cooperative        or passive in relation to the AIS system,    -   it allows to broadcast geolocated information that is useful for        navigation and safety, such as local weather, sea conditions or        hazards not marked on maps,    -   it uses existing means already deployed in operational systems        (AIS, satellite links), with no risk of saturating these means,    -   at any moment, a user of an AIS terminal can switch between a        standard AIS mode and an extended AIS mode, if the summary        information is marked as such,    -   it allows for the broadcasting by AIS channel of        extended/augmented context information to ships not necessarily        equipped with satellite links,    -   the monitoring of broadcasting makes it possible to detect an        occasional or lasting failure of a ship configured as reference        station, the system can then remove its reference status (until        a new command), and schedule new resources,    -   any ship provided with an AIS transponder can check the        operation of its transponder, relative to its GPS and to the        extended context information,    -   the system can facilitate the reception of AIS signals acquired        onboard a satellite or an aircraft, effected by a large number        of interfering AIS messages, by providing exact information on        all the AIS messages transmitted by the ships controlled by the        system, to further extend the coverage (ships outside the        coverage of the system, and with no satellite link).

The invention claimed is:
 1. A system for augmenting a range of anexisting Automatic Identification System (AIS) system, said systemcomprising: communication means to exchange information between one ormore elements forming said system; one or more land-based processingcentres comprising: communication interfaces to exchange informationwith different users, to receive information from reference ships, andfrom one or more coastal stations, and to broadcast consolidated andextended information after processing to said reference ships andcoastal stations, which will relay to other ships via the AIS channel, aset of processors suitable to merge information of different types foraggregating the AIS data originating from all the ships within AIS rangeof the reference ships or the coastal stations, with other data, one ormore databases, and a memory to store information to be processed; meansfor determining dynamically reference ships and associated service; theone or more coastal stations being equipped with an AIS transceiver andbeing linked with the one or more land-based processing centres by thecommunication interfaces, allowing for an exchange of information; oneor more ships equipped with AIS transceiver and satellite communicationmeans, eligible as the reference ships by the land-based processingcentres controlling an area where the one or more ships are located fora given time period, said reference ships communicating with theland-based processing centres by satellite means, and with other shipswithin the VHF range by the AIS system; and at least two ships,different from the reference ships, provided at least with an AISreceiver to retrieve the extended information broadcast by a referenceship or reference coastal stations within VHF range.
 2. The systemaccording to claim 1, wherein one or more of the land-based processingcentres has one or more of the communication interfaces for receivinggeo-referenced observation/detection data, and said set of processors isconfigured to aggregate the received gee-referencedobservation/detection data from different ones of the reference shipsand the coastal stations having the geo-referenced observation/detectiondata.
 3. The system according to claim 1, wherein one or more of theland-based processing centres further comprises: a first database in theone or more databases configured to store information specifically foridentifying a ship, said information chosen from the following list: theship's position, the ship's heading, the ship's speed, the ship's rateof turn, the ship's route, the ship's scheduled departure date and time,the ship's scheduled arrival date and time; and a second database in theone or more databases comprising information from radar and opticalobservations.
 4. A method for augmenting a range of an existingAutomatic Identification System (AIS)-type system, the methodcomprising: defining, using a land-based processing centre havingprocessors, one or more reference coastal stations in a plurality ofcoastal stations, and one or more reference ships in a plurality ofships; the land-based processing centre controlling a coverage area,such that for each time period or time slice of a given duration in aplurality of time periods or time slices; retrieving and accumulatingone or more current local AIS contexts, for a particular time periodconcerned, detected by reference stations, comprising at least areference ship or a reference coastal station, coming under the coveragearea of the land-based processing centre; consolidating AIS information,for each local AIS context, by incorporating in a database, newinformation specific to said plurality ships comprising informationassociated with a ship identification parameter, a position, a heading,and a speed; formatting for each reference station that broadcasts theinformation: for a configured visibility radius, formatting a specificdatabase taking information on objects in a global context database,within a given radius from the reference station that is scheduled forthe broadcast; transmitting said formatted information to said referencestation, via satellite links or via terrestrial communication means;broadcasting global context information in the global context databaseto users on land by using the terrestrial communication means; for thereference ship, collecting the local AIS context and transmitting to theland-based processing centre via satellite link; broadcasting anextended context via an AIS-type channel to the ships or the objectsequipped with an AIS-type receiver located within a cell defined by aVery High Frequency (VHF) range; for the reference coastal station,collecting the local AIS context and transmitting to the land-basedprocessing centre via the terrestrial communication means; broadcastingthe extended context via the AIS-type channel to the ships or theobjects equipped with the AIS-type receiver located within the celldefined by the VHF range.
 5. The method according to claim 4, wherein,in the land-based processing centre, the global context information ismerged with available complementary data associated with at least one ofradar data, optical observation data, or text messages concerning thelocation of new hazards such that the reference stations associated withan AIS cell further broadcast the merged information.
 6. The methodaccording to claim 5, wherein the merged information comprisesgeolocated information on weather conditions and sea conditions.
 7. Themethod according to claim 4, wherein, for the land-based processingcentre controlling the coverage area, the method comprises executing ascheduling algorithm for the reference stations, said schedulingalgorithm comprising: initialisation by a declaration of the coastalstations as the reference stations, looping, at a rate equal to the timeperiod: a projection of the position of the ships managed by theAIS-type system: for each ship in the plurality of ships, for eachfuture time period, up to a prediction horizon for the ship, projectingthe position, the speed and the heading, given information regardingpredicted date and time of departure, of arrival, route, and lastsignalling, a determination of eligible ships in the plurality of ships,which can be defined as the one or more reference ships: for each saidfuture time period, for each ship in the plurality of ships, if the shiphas a projected trajectory that departs from the coverage area definedfor the time period, then it is eligible to be defined by the land-basedprocessing centre as one of the reference ships, a selection of thereference ships carried out by iterating, for the desired redundancylevel for each said future time period for each eligible ship, searchingto determine if other eligible ships are in the immediate vicinitydefined by the VHF range, and selecting a best eligible ship accordingto one or more criteria comprising: whether the ship is a commercialship, a pricing, a course, a limitation on changes of configuration foreach ship, removing the selected ship from a list of eligible ships, andupdating definition of the coverage area, withdrawing the referenceships: for each said future time period, for each reference ship,searching to determine if other reference ships or reference coastalstations are in the immediate vicinity, identifying N best referenceships or reference coastal stations, where N is an integer defining thedesired redundancy level, removing the unselected ships from the list ofeligible ships, and updating the definition of the coverage area.
 8. Themethod according to claim 7, further comprising: scheduling thereference stations to collect the local AIS-context information, and tobroadcast the consolidated global context information; solely collectingthe local AIS-context information; solely rebroadcasting theconsolidated global context information; checking a correctness of therebroadcasting of the consolidated global context information by anotherreference station.
 9. The method according to claim 4, furthercomprising: detecting inconsistencies in the transmitted formattedinformation, or a failure in an operation of the communications for agiven ship, wherein two ships that are in the VHF range, within the samecell, are selected, such that the land-based processing centre whichcontrols the cell within which the ships are located decides that afirst of the two ships will monitor the information relating to thecoverage area derived from the global context information transmitted bya second of the two ships, the land-based processing centre transmittingsame consolidated information to the two ships, if the first ship isconfigured to monitor the information transmitted by the second ship,the first ship monitors the consolidated information that the secondship broadcasts via the AIS-type channel to other ships in VHF range, aterminal of the first ship implementing a means for determining anidentity of the second ship and content of the information that thesecond ship broadcasts.
 10. The method according to claim 4, furthercomprising: checking consistency of the AIS information transmitted by aship, wherein when the ship broadcasts an AIS message containingincorrect position information, the AIS-type system detects that theposition is not correct, when this position does not geographically comeunder the cell of the ship or of the reference station that picks up theAIS message, or when the AIS message has not been picked up by anotherreference station or another reference ship close to a declared positionof the reference ship.